1. Field of the Invention
This invention is generally related to the field of well logging and more particularly to the use of downhole tools to determine the orientation of formation in-situ stresses.
2. Prior Art
Formations in the earth are characterized by stress fields which vary with depth and whose principal directions are vertical and horizontal. In the horizontal plane at any point, the horizontal stress field reaches a maximum in one direction and a minimum at right angles to the first direction. Information concerning these maximum and minimum horizontal stress directions is of substantial value in planning field exploitation both where hydraulic fracturing is to be employed for stimulation and where directional drilling is to be employed to exploit systems of natural fractures.
One prior art method for identifying formation in-situ stress orientation requires hydraulically fracturing the formation and deducing the orientation of such fracture through wellbore or surface measuring techniques. This is a prohibitively expensive method of collecting data. Another prior art method adapted to naturally fractured formations utilizes a downhole televiewer to view a fracture. This method only works if the wellbore intersects a natural fracture and is thus dependent for its success upon pure chance.
It is a general object of this invention to devise an improved method and apparatus for identifying formation in-situ stress orientation.
It is a more particular object of this invention to devise a downhole method and apparatus for the purpose indicated above which allows measurements to be taken at any number of depths during a single run.
It is a still further object of this invention to devise a downhole method and apparatus for the purpose indicated above which offers the economy and convenience of a wire line technique.